Treatment of fabrics



Patented Aug. 16, 1938 UNITED STATES TREATlVIENT OF FABRICS Cornelius A.Alt, Newburgh, N. Y., assignor to E. I. du Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware No Drawing. ApplicationDecember 19, 1935, Serial No. 55,198

4 Claims.

This invention relates to a method for treating fabrics and moreparticularly to a method for treating fabrics which are to be coatedwith cellulose derivative coating compositions and 5 which are subjectedto sunlight exposure in service.

. Cellulose derivative coated fabrics ofvarious types are extensivelyused for many purposes but possess certain limitations for specializeduses 10 such as window shade materials or other materials which arecontinuously exposed to sunlight. Cellulose derivative coated fabricswhich are subjected to prolonged exposure to actinic rays are subject todeterioration of the coating composition and of the base fabric. InUnited States of America Letters Patent 2,033,170, issued March 10,1936, is disclosed a means of overcoming or reducing to a minimum thedeterioration of the material when placed in service by the use ofleaded zinc oxide in the coating composition.

The shade cloth therein described represents a great improvement overthe prior art. One phase of the present invention represents a methd ofproducing a shade cloth having exceptionally long life in a differentmanner.

z I have found that such further improvements may be made in cellulosederivative coated fabrics particularly those used for shade cloth whichare subjected to prolonged exposure to actinic rays 30 and suchimprovements are embodied in the present invention.

This invention has as an object the provision of a process for producingimproved cellulose derivative coated fabrics which are characterized 35by improved resistance to aging upon exposure to sunlight.

A further object is the provision of a process for producing improvedcellulose derivative fabrics useful for shade cloth which exhibitsimproved resistance to tendering upon prolonged exposure to sunlight.

These and other objects which will appear hereinafter are accomplishedby impregnating a fabric with a material which may be described as anacid acceptor preliminary to the application of the coating composition.

In cellulose derivative coated fabrics, particularly those usingcellulose nitrate, the bond or anchorage of the coating composition witha base fabric is favored by the projecting loose ends of the fibers ofthe yarns being embedded in the film of the coating composition. Thesefibers would be readily weakened or destroyed by the liberation ofcertain deleterious agents originating from a decomposition of thecellulose nitrate. Such a weakening or destruction of the loose endfibers weakens or destroys the bond or anchorage of the film to the basefabric. In time the weakening of the fibers extends further andeventually weakens the yarns resulting in a general tendering of theentire fabric. The present invention which overcomes the tendency of theweakening or destruction of the loose end fibers and such yarns of thefabric is best illustrated by the following description of the processfor treating the fabric.

The sheet material which is later to be coated is impregnated by passingit through a thin aqueous slurry of such a material as zinc oxide and isthen passed through or between suitable rolls to remove the excess ofthe slurry and finally is dried by contacting it with heated air. A dyepadding machine has been'founduseful for the impregnating stepespecially so since such a machine has attached to it suitable rolls forpressing out the excess material.

The zinc oxide preferred for use is that known in the trade as Kadox andproduced according to the process disclosed in U. S. Patent 1,522,096.The particles of this particular zinc oxide are described as beingcolloidal in nature and measurements reveal them to have an average sizeof the order of 12 microns, and practically all the particles arebetween 10 and 20 microns in size.

The impregnating medium is prepared by grinding 1 part of the Kadoxdescribed above with 2 parts of water in a suitable ball mill for aperiod of approximately 2 hours. A viscous paste is thus produced. Thispaste is then added to a sufficient quantity of water to produce aconcentration of approximately 5% of dry zinc oxide.

By using a slurry with a zinc oxide concentration of approximately 5%and further using normal padder conditions the fabric will gain about70% in water and zinc oxide. Since the usual limits are from 50% to 100%of the fabric by the impregnating media, 100 lbs. of cloth will beimpregnated with about 3.5 lbs. dry zinc oxide. The amount of water andzinc oxide which is taken up by the fabric can be varied and controlledwithin limits by a control of the pressure applied on the squeeze rolls.

After the fabric has been impregnated and dried as noted above it iscoated with a cellulose derivative coating composition by means of adoctor knife or any other suitable means well known to those skilled inthe art of coating fabrics. A suitable coating composition to be appliedto fabric is:

Any commercial zinc oxide, pure or leaded; may be used but the Kadoxmaterial with a lead content varying between limits of 0.5-1.0%expressed as lead oxide is preferred. Although best results accrue withthe use of colloidal zinc oxide, other materials such as zinc hydroxide,5% leaded zinc oxide, calcium hydroxide, aluminum hydroxide, zincacetate, ammonium borate, etc., yield satisfactory results when used incombination with zinc oxide.

The concentration of the zinc oxide for example in the impregnatingslurry may vary from very small concentrations such as 1% to aconcentratlon of as high as 20%. However a concentration ofapproximately 5% is preferred as it yields most satisfactory resultsfrom a practical standpoint. Concentrations lower than 1% as well asconcentrations above are not preferred because the former requiresseveral impregnating treatments and the latter deposits too great anamount of zinc oxide in the fabric causing dusting after the materialhas dried.

If desired the impregnation operation may be carried out in connectionwith the bleaching operation of the fabric. Under such conditions it isnot necessary to dry the fabric before impregnating, although a slightlyhigher percentage of zinc oxide in the impregnating medium is necessary.Modifications in connection therewith are such as will be readilyapparent to those skilled in the art and are well within the purview ofthe present invention.

The treatment described herein is not limited to any particular type offabric but to all such types of fabrics as are usually coated as, forexample, sheetings, ducks, canvas, drills, sateens, moleskin, brokentwills, etc.

The, principal advantage of the invention is the production of coatedfabrics which are superior to material made according to the presentstate of the art with respect to the life of the coated fabric asdetermined by tendering in service. It has been found that the tenderingof cellulose nitrate coated fabrics particularly such as are used forshade cloth can be retarded to such an extent that the life of thematerial as determined by accelerated tests may be prolonged from 12 to20 weeks. This represents a life increase of at least 60% by treatmentof the fabric as described in the present invention which whentransposed into years of normal service is remarkable. A furtheradvantage is the improved anchorage or bond of the coating tothe fabricwhich greatly increases the life of such bond or anchorage when thematerial is placed in service.

It is apparent that many widely different embodiments of this inventionmay be made without departing from the spirit and scope thereof; and,therefore, it is not intended to be limited except as indicated in theappended claims.

I claim:

1. The process of preparing shade cloth which comprises the improvementof applying directly to an uncoated cloth a composition containing anacid acceptor consisting substantially of colloidal zinc oxide, removingall of the ingredients of the said composition except the acid acceptor,and thereafter applying a cellulose derivative coating.

2. Process of preparing shade cloth which comprises impregnating anunfilled fabric base with a 5% slurry of zinc oxide, the particlesizeoi'whichis between 10 and 20 microns in diameter, removing theexcess slurry by passing the impregnated fabric through squeeze rolls,drying the treated fabric, and applying to at least one surface of thefabric a composition comprising cellulose nitrate pigment andplasticizer.

3. Process ofpreparing shade cloth which comprises impregnating anunfilled fabric base with a 5% slurry of colloidal zinc oxide, dryingthe fabric, and applying thereto a composition having the followingformula:

Parts by weight Cellulose nitrate 15 Pigment 22.6 Plasticizer 11.3 Ethylacetate 20.4 Ethyl alcohol 30.7

4. Shade cloth having a fabric base containing zinc oxide and acellulose nitrate composition coating, obtainable by impregnating anunfilled fabric base with a 5% slurry of colloidal zinc oxide, dryingthe fabric, and applying thereto a composition having the followingformula:

Parts by weight Cellulose nitrate 15 Pigment 22.6 Plasticizer 11.3 Ethylacetate 20.4 Ethyl alcohol 30.7

CORNELIUS A. ALT.

